The general objectives of the study are (1) to achieve the complete growth and development of parasitic nematodes in culture through successive generations, and (2) to use culture methods as a tool for the study of developmental and physiological processes of the parasite. Specifically, the study will focus on the growth requirements of two trichostrongyle nematode parasites of rodents, Nippostrongylus brasiliensis and Nematospiroides dubius. Both species have already been cultured through most or all of their life cycle. Further studies will attempt to obtain mating and the production of viable eggs on a consistent basis, and subsequently the continuous cycling of the parasite in vitro. Studies on the free-living phase of development will exploit specific bacteria, particularly auxotrophic mutants to obtain information on nutritional requirements. Further characterization will be made of a growth inhibitor for larvae, present in the feces of germfree mice. The relation of vitamin B12 to nematode development will be studied in vitro and in vivo. In particular, attempts will be made to determine whether coelomocytes of larvae, which have an extraordinary capacity to concentrate B12, function as a storage depot for the vitamin, and later release it to rapidly differentiating tissues of the nematode during the parasitic cycle of development. Exploration of the possible role of coelomocytes in the regulation of nematode growth will be undertaken. Biochemical and physiological studies as they relate to the developmental biology of these nematodes will be undertaken. Also, other helminths, such as cestodes, will be used for comparative purposes, particularly for investigations on vitamin B12.